A Manitoba MP has quit the New Democratic Party, saying her stand against same-sex marriage has cost her the party's nomination in the next federal election.

Bev Desjarlais sat as an Independent in the House of Commons on Tuesday, after representing the Churchill riding since 1997 as an NDP.

Desjarlais was the only NDP member to vote against the same-sex marriage bill earlier this year, and was subsequently stripped of her critic's duties. She told CBC News she expected her nomination to be challenged.

"It's cost me in the sense of there was a challenge and I lost the nomination. It hasn't cost me in the sense of feeling comfortable in where I am on making a conscience decision," she told CBC News.

"Hopefully the people in the Churchill riding will recognize that they have an MP who will stick to her word, will do the job and will be honest and upfront. That's what I've offered for almost nine years now, and hope to continue offering after the next federal election."

Desjarlais says she plans to run as an Independent in the next federal election.

Until then, "it will certainly be my intention to vote on each issue as it comes up," she said. "And if it's areas where I believe in what's before the House and know that that's what the riding wants me to do, that's what I'll be doing."

Desjarlais leaves the NDP caucus at a time when the party is trying to squeeze more concessions out of the Liberals in exchange for supporting Paul Martin's minority government.

Her departure will leave the NDP with 18 seats in the House of Commons. The Liberals have 133 seats, the Conservatives 98 and the Bloc QuÂ¿bÂ¿cois 54. Three other Independents also sit in the House.

MLA's daughter to represent NDP in next election

Niki Ashton, 23, won the NDP nomination in the Churchill riding, coming out ahead of Desjarlais and two other candidates.

Ashton says she doesn't believe Desjarlais' stance on same-sex marriage is totally responsible for her loss in the nomination vote.

"It wasn't a matter of running against any particular person," Ashton said. "It was more a matter of putting ahead a forward agenda for the North for the Churchill riding, an agenda that basically asks for national attention on issues of importance to northerners, issues such as the third-world living conditions that many of our communities face, [such as] appalling health issues."

Ashton, who was born and raised in Thompson, says politics are her passion. It must run in the family: her father is Manitoba NDP cabinet minister Steve Ashton.